Various types of foulants pose problems during production and refining of hydrocarbon fluids. Foulants are materials within the production fluid that may become destabilized and agglomerate to each other and deposit on equipment, which can cause problems with the fluid during extraction, transporting, processing, refining, combustion, and the like. Examples of foulants include asphaltenes, iron sulfides, waxes, coke, sand, ores, clays, hydrates, naphthenates and the like.
Asphaltenes are most commonly defined as that portion of petroleum, which is soluble in xylene and toluene, but insoluble in heptane or pentane. Asphaltenes exist in crude oil as both soluble species and in the form of colloidal dispersions stabilized by other components in the crude oil. Asphaltenes have higher molecular weights and are the more polar fractions of crude oil, and can precipitate upon pressure, temperature, and compositional changes in crude oil resulting from blending or other mechanical or physicochemical processing. Asphaltene precipitation and deposition can cause problems in subterranean reservoirs, upstream production facilities, mid-stream transportation facilities, refineries, and fuel blending operations. In petroleum production facilities, asphaltene precipitation and deposition can occur in near wellbore reservoir regions, wells, flowlines, separators, and other equipment. Once deposited, asphaltenes present numerous problems for crude oil producers. For example, asphaltene deposits can plug downhole tubulars, wellbores, choke off pipes and interfere with the functioning of safety shut-off valves, and separator equipment. Asphaltenes have caused problems in refinery processes such as desalters, distillation preheat units, and cokers.
Many formation fluids, such as petroleum fluids, contain a large number of components with very complex compositions. For the purposes herein, a formation fluid is the product from a crude oil well from the time it is produced until it is refined. Some of the potentially fouling-causing components present in a formation fluid, for example asphaltenes, are stable in the crude oil under equilibrium reservoir conditions, but may aggregate or deposit as temperatures, pressures, and overall fluid compositions change as the crude oil is removed from the reservoir during production. Waxes comprise predominantly high molecular weight paraffinic hydrocarbons, i.e. alkanes. Asphaltenes are typically dark brown to black-colored amorphous solids with complex structures and relatively high molecular weights.
In addition to carbon and hydrogen in the composition, asphaltenes also may contain nitrogen, oxygen and sulfur species, and may also contain metal species such as nickel, vanadium, and iron. Typical asphaltenes are known to have different solubilities in the formation fluid itself or in certain solvents like carbon disulfide or aromatic solvents, such as benzene, toluene, xylene, and the like. However, the asphaltenes are insoluble in solvents like paraffinic compounds, including but not limited to pentane, heptane, octane, etc. Asphaltene stability can even be disturbed by mixing hydrocarbon-based fluids i.e. such as mixing two types of crude oils together, two types of shale oils together, condensates, and others, of different origins at certain ratios as the chemistry of the hydrocarbon-based fluids from different sources may be incompatible and induce destabilization of the asphaltenes therein. In non-limiting examples, such as during refining or fuel blending, two or more hydrocarbon-based fluids may be mixed together. Sometimes, changes in physical conditions are sufficient to induce destabilization, or even the mixture of different hydrocarbon-based fluids that have incompatible chemistries. Said differently, even if neither hydrocarbon-based fluid, alone, has destabilized foulants or the hydrocarbon-based fluid would not act as a destabilizing additive by itself, the mixing or the mixture of two or more hydrocarbon-based fluids may further destabilize the foulants present in either hydrocarbon-based fluid.
When the formation fluid from a subsurface formation comes into contact with a pipe, a valve, or other production equipment of a wellbore, or when there is a decrease in temperature, pressure, or change of other conditions, foulants may precipitate or separate out of a well stream or the formation fluid, while flowing into and through the wellbore to the wellhead. While any foulants separation or precipitation is undesirable in and by itself, it is much worse to allow the foulant precipitants to accumulate and deposit on equipment in the wellbore. Any foulant precipitants depositing on wellbore surfaces may narrow pipes and clog wellbore perforations, various flow valves, and other wellsite and downhole locations. This may result in wellsite equipment failures and/or closure of a well. It may also slow down, reduce or even totally prevent the flow of formation fluid into the wellbore and/or out of the wellhead.
Similarly, undetected precipitations and accumulations of foulants in a pipeline for transferring crude oil could result in loss of crude oil flow and/or equipment failure. Crude oil storage facilities could have maintenance or capacity problems if foulant precipitations occur. These fluids also carry unstable foulants into the refinery, as well as possibly into finished fuels and products where the foulants cause similar problems for facilities of this nature.
Accordingly, there are large incentives to mitigate fouling during refining. There are large costs associated with shutting down production units because of the fouling components within, as well as the cost to clean the units. The foulants may create an insulating effect within the production unit, reduce the efficiency and/or reactivity, and the like. In either case, reducing the amount of fouling would reduce the cost to produce hydrocarbon fluids and the products derived therefrom.
One technique to reduce the adverse effects of foulants within the formation fluid is to add a foulant inhibitor to the hydrocarbon-based fluid having potential fouling causing components. A ‘foulant inhibitor’ is defined herein to mean an inhibitor that targets a specific foulant. Several foulant inhibitors may be added to reduce the adverse effects of each type of foulant, e.g. asphaltene foulant inhibitors, iron sulfide foulant inhibitors, etc.; all may be added to the fluid to decrease the adverse effects of each type of foulant, such as deposition, accumulation, and/or agglomeration of the foulant(s). However, it has been difficult to analyze the stability or efficacy of the foulant inhibitors because the experimental conditions may not always represent actual ‘field’ conditions of the formation fluid.
There are several shortcomings when measuring foulant stability and/or efficacy of a foulant inhibitor to improve foulant stability. Thus, it would be desirable to develop better methods of analyzing the stability of the foulants and/or foulant inhibitors.